Various applications demand high-quality large-sized glass sheets. Examples include liquid crystal displays (LCD), other types of flat panel displays, e.g., plasma displays, field emission displays, and organic light-emitting polymer displays, and photovoltaic panels. Fusion draw process is one of the few processes capable of delivering glass sheets without requiring costly surface post-forming finishing operations such as lapping and polishing. Fusion draw process is described in U.S. Pat. No. 3,682,609 (hereinafter the “'609 Patent”) and U.S. Pat. No. 3,338,696 (hereinafter the “'696 Patent”). Typically, the fusion draw process involves delivering molten glass into a trough and overflowing the molten glass down the sides of the trough in a controlled manner. The separate streams of molten glass flowing down the sides of the trough merge at the root of the trough into a single stream of molten glass, which is drawn into a continuous glass sheet. The continuous glass sheet is separated into discrete pieces at the bottom of the fusion draw machine. A key advantage of this process is that the surfaces of the glass sheet do not come in contact with the sides of the trough or other forming equipment and therefore are pristine (See col. 1, lines 45-50 of the '696 Patent). Another benefit of the process is that the drawn glass sheet can have a uniform thickness (See the '609 Patent).
Post-forming operations include cutting the glass sheets into desired shapes and sizes. Cutting is typically by mechanical scoring. As-cut square glass sheet edges chip easily and have low impact strength. Due to the nature of glass, a tiny crack at an edge of the glass sheet can propagate across the glass sheet, rendering the glass sheet useless. The traditional approach to avoiding damage to the cut glass sheet is to finish the as-cut edges of the glass sheet by grinding and/or polishing. In addition to being expensive, this approach often generates micron-sized glass particles that can contaminate the quality surfaces of the glass sheet. The quality surfaces are required to have a high degree of cleanliness and be free from scratches. Extensive washing and drying at the end of the finishing process are needed to clean and wash off the generated particles. In some cases, some of these particles can irreversibly adhere to the clean glass surface, rendering the glass sheet useless for many applications.
Laser scoring can create better as-cut edges than mechanical scoring. However, as-cut square edges, even if produced by laser scoring, will typically not have the impact strength necessary to avoid damage to the glass sheet in down-stream glass handling and processing steps. The key challenge is to provide a high-strength edge without subsequent finishing processes such as grinding, polishing, and washing. Patent application publication No. US 2005/0090189 (Brown et al.) describes a removable grinding shroud that may be used to protect the surfaces of the glass sheet from generated particles during grinding of the as-cut edges of the glass sheet. The grinding shroud is detached from the glass sheet once the grinding process is completed and not used when the edges of the glass sheet are polished. The edge finishing process is costly, and even with a shroud technology, it is difficult to finish the glass sheet without depositing particles on the glass surface.